Magnetic-type EAS systems are widely used to inhibit the theft of merchandise such as clothing, books, cassettes and compact disks. Electronic article surveillance (EAS) systems are often used to prevent unauthorized removal of articles from a protected area, such as a library or retail store. An EAS system usually includes an interrogation zone or corridor located near the exit of the protected area and markers or tags attached to the articles to be protected. EAS systems have been based on magnetic, RF, microwave and magneto-restrictive technologies. Regardless of the particular technology involved, the EAS systems are designed such that the tag will produce some characteristic response when exposed to an interrogating signal in the corridor. Detection of this characteristic response indicates the presence of a sensitized tag in the corridor. The EAS system then initiates some appropriate security action, such as sounding an audible alarm, locking an exit gate, etc. To allow authorized removal of articles from the protected area, tags that are either permanently or reversibly deactivatable (i.e., dual status tags) are often used.
Although EAS markers have been in common use for the theft protection of optically recorded media such as compact disks and CD-ROM's, the markers have generally been adapted for attachment to the packages containing new compact disks and have been poorly suited for direct attachment to the compact disk itself For libraries and other institutions that repeatedly check compact disks in and out to accommodate the needs of customers and clients, effective inventory control would prefer that EAS markers are attached to the compact disk.
Some markers for direct attachment to compact disks have been developed. One, available as "DCD-1" from Minnesota Mining and Manufacturing Company, St. Paul, Minn., is a single marker strip and security overlay which are attached to a compact disk. However, this marker adversely effects the mechanical balance of the disk, which can adversely affect the operation of modern high rotation speed CD-ROM drives, CD players, and other optically recorded media playback equipment which require that the media be mechanically balanced for proper operation. Another product, "CD-Guard", available from Knogo North America, Inc., Hauppauge, Long Island, N.Y., suffers the same mechanical balance drawback. An optical information storage disk comprising an embedded, generally annular, dual-status EAS marker is described in coassigned U.S. Pat. No. 5,347,508.
There is therefore a need in the art for a marker specifically designed for protection of optically recorded media.